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  <h1>Object.defineProperty——vue的响应式原理</h1>
  <input type="text" id="input">
  <p id="p">
    <span>输入框的值为：</span>
    <span id="span"></span>
  </p>
  <script>
    let obj = {val: ''};
    Object.defineProperty(obj, 'val', {
      // 存取描述符-set
      set(newValue) {
        span.innerHTML = newValue;
      },
      // 存取描述符-get
      get() {

      }
    })
    // let input = document.getElementById('input');
    input.onkeyup = function inputChange() {
      obj.val = input.value;
    }
  </script>
</body>
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